Calciferous and similar deposits occur in body fluid passages of various types. Of particular interest are urinary and biliary calculi as well as arteriosclerotic plaque.
Electrohydraulic lithotripsy and laser lithotripsy systems frequently are used to fragment urinary and biliary stones. Both systems utilize plasma-induced stress waves to fragment calculi. Electrohydraulic lithotripsy produces a plasma through an electrical discharge (spark). Electrohydraulic lithotripsy systems are relatively inexpensive. However, with electrohydraulic lithotripsy systems, there is a potential for thermal damage to healthy tissues surrounding the target deposit. With laser lithotripsy, a plasma is produced when a portion of the laser energy is absorbed by the stone. However, laser lithotripsy systems are expensive. Also, in the case of laser lithotripsy, the sharp laser delivery fiber may cause damage if inadvertently jabbed into healthy tissue.
In my article with Rosen et al entitled "Effects of Shielded or Unshielded Laser and Electrohydraulic Lithotripsy on Rabbit Bladder" published in the Journal of Urology, Vol. 148, Pages 857-860, April 1990, I disclosed a plasma shield for use with either a pulsed laser lithotriptor or an electrohydraulic lithotriptor. As described therein, the hollow shield is provided using a hollow spring fitted with a metal end cap. The pulsed laser source or pulsed electrical voltage source located in the flexible guide provides a pulse of energy in the vicinity of the metal end cap to produce a rapid vapor expansion that causes the metal end cap to undergo a pulse-like movement as the vapor expands against the fluid medium of the passage to impart a high-velocity jack-hammer type impact on the target deposit.
While the plasma shield impact device as described in my aforesaid publication offers the advantages of protecting surrounding healthy tissue from direct laser/EHL spark, and also eliminates inadvertent puncturing of healthy tissue by a sharply pointed laser delivery fiber, the metal end cap is prone to fragmentation, resulting in the formation of metal fines in the body cavity.